Process for stripping spent catalyst



Oct. 7, 1947. c. w. TYSON PROCESSFOR STRIPPING SPENT CATALYST Filed June10, 1944 5 in II nu mm n OPU(UU dobauzmomu uaui Char/e5 51'. 7515011Unvenbor H l Clbbbrnaq Patented Oct. 7, 1947 rnocass FOR s'rmrrmo SPENTCATALYST Charles W. Tyson, Summit, N. 1., assignor to Standard OilDevelopment Company, a corporation of Delaware Application June 10.1944, Serial No. 539,704

6 Claims. (Cl. 196-52) This invention relates to a method of treatingases and solids wherein carbonaceous materials are subjected toconversion in the presence of subdivided solid contact material which iscontinuously circulated through a conversion zone, and pertains moreparticularly to a method of and apparatus for removing volatilizableconversion fluids from the solid contact material withdrawn from theconversion zone.

While the invention in some of its broader phases may have a moregeneral application, it is particularly adapted for the conversion ofhydrocarbon oils and particularly for the catalytic cracking of suchoils wherein the oil is converted in the presence of subdividedcatalytic material which is continuously circulated through a conversionzone and thereafter through a regenerating zone in which combustibledeposits formed during the conversion treatment are burned from thecatalytic material and the catalytic material so regenerated thenreturned to the conversion zone.

According to one general type of process commonly known as the fluidprocess, the catalytic material in finely divided form is circulated ina fluidized state through the cracking and regenerating zones and thepressure lost during the circulation is restored by passing thecatalytic material'through a vertical column or standpipe containing arelatively dense mass of finely divided catalytic material maintained ina fluid state by injecting a small amount of a fiuidizing gas into thematerial passing through the column. The amount of such fiuidizing gasso introduced is normallyv maintained at the minimum suflicent toconvert the powder into a fluid state capable of generating a fiuidpressure at the base of the column.

According to previous practices the aerating gas introduced into thecolumn or standpipe comprised in general an inert gas such as steam orspent combustion gases.

According to another general type of process the catalyst in arelatively coarse. granular form is gravitated downwardly through theconversion zone and the regenerating zone and is conveyed from the baseof one of said zones to the top of the other by mechanical conveyors.

In both modes of operation the catalytic material removed from theconversion zone contains substantial quantities of volatile combustiblematerial which not only increases the amount of heat liberated duringregeneration but may also reduce the overall yield of valuable productsproduced during the conversion treatment. It has been proposedheretofore to subject the catalytic material withdrawn from suchconversion zone to the action of an inert stripping gas such as steam orspent combustion gases. In many cases, however, the use oi steam has aharmful effect on the catalytic material and the use of inert spentcombustion gases normally requires the installation of an inert gasproducer, thereby increasing the cost of the equipment. One of thebroader objects of the present invention is to provide an improvedmethod of removing the volatilizable reaction products from thesubdivided solids withdrawn from the reaction or conversion zone.

A more specific object of the invention is to provide an improved methodof stripping or removing volatilizable reaction products from finelydivided solid material which is circulated in a fluid state through theconversion and regen erating zones.

Other more specific objects of the invention will be apparent from thedescription hereinafter wherein reference will be made to theaccompanying drawing illustrating the invention as applied to the fluidprocess for the cracking or conversion of hydrocarbon oils.

Referring to the drawing, the reference character l0 designates a chargeline through which which is to be subjected to reforming or refining,

or it may comprise a higher boiling stock such as gas oils or reducedcrudes which are to be sub- Jected to the conversion process.

The oil passing through line It may be at room temperature or it mayhave been subjected to initial preheating. The oil passing through lineIll is intermixed with a stream of finely divided conversion catalystdischarging through vertical conduit H having a control valve l2 forregulating the amount of catalytic material introduced into the stream.The catalytic material so introduced may be an active cracking catalystsuch as activated clays or synthetic absorbent materials of the same ordifferent composition. Various types of cracking catalysts haveheretofore been proposed for this purpose. The catalyst dischargingthrough the conduit ll into the oil stream is withdrawn directly rromregenerator l3 positioned thereabove and is at substantiallyregeneration temperature. The amount of catalyst introduced may becontrolled so that the heat from the catalyst is suflicient to supplythe necessary heat for the conversion process. For

3 example, the regenerator may be at a temperature of the order of from1000 F. to 1200 F. The amount of catalyst introduced may be of the orderof from one part of catalyst per part of oil I by weight to 25 or moreparts of catalyst per part of oil, depending upon the nature of theconversion, the activity of the catalyst, and other factors.

The catalytic material passing through the vertical conduit II ismaintained in a fluid state by the injection of a small amount offluidizing gas at one or more spaced points through lines I4, I5 and I6.The amount of gas in this case is limited to the minimum necessary tomaintain the catalytic material in a fluid state capable of generating afluid pressure at the base of the column. Under ideal conditions theamount of gas introduced through lines I4, I5 and I6 is just sufficientto compensate for the compression of the gas associated with thecatalyst particles passing downwardly through the standpipe or column IIso that the density in pounds of catalyst per cubic foot issubstantially uniform throughout the full length of the column. Underthese conditions the maximum amount of pressure can be generated withthe minimum length of conduit H. This is desirable because in theconstruction illustrated the regenerator is constructed above thestandpipe and it is desirable for economic reasons to keep theregenerator at the lowest elevation possible.

The fiuidizing gas introduced through lines I4, I5 and I6 may compriseany' inert gas such as steam or spent combustion gases but preferablycomprises air. The catalytic material passing through the conduit IInormally contains a small amount of residual carbonaceous material notremoved from the catalyst during regeneration in the regenerator I3. Theamount of carbonaceous deposits contained on the catalyst is normallysuflicient to react with the air introduced through lines I4, I5 and I6and consumes substantially all of the free oxygen contained therein sothat the gas entrained with the catalyst discharging into the oil streamis substantially devoid of free oxygen. The invention in its broaderphases, however, is not limited to the type of gas introduced into theconduit I I.

The suspension of catalyst and oil formed in the conduit II continuesthrough. line I! and is introduced into the bottom of reactor I8 througha distributing cone I9 having a perforated grid for distributing thesuspension throughout the reactor. The distributing cone I9 ispreferably spaced from the wall of the reactor I8 as illus- 'trated toprovide an annular passage for the removal of catalytic material fromthe reactor, as later described. The reactor I8 is preferably designedof such diameter that the velocity of the oil vapors passing upwardlythrough the reactor is reduced to such a point as to cause the finelydivided catalytic material to separate into a relatively dense layer inthe bottom portion thereof. The superficial velocity of the vapors toaccomplish this purpose may be of the order of from 1 to 3 feet persecond when employing finely divided catalytic material having aparticle size below about 400 mesh and an apparent density below 1.0.The passage of the vapors upwardly through the reactor I8 maintains thecatalytic material in a turbulent state so that a substantially uniformtemperature is maintained throughout the reactor. The level of theturbulent bed of catalytic material within the reactor l8 above thepoint of introduction of the oil vapors therein is controlled ashereinafter described to provide the required contact time between theoil vapors and catalyst for producing the desired conversion. Thiscontact time, in the case of catalytic cracking, may be of the order offrom 5 to 50 seconds.

The weight space velocity as expressed by the weight of oil passingthrough the reactor per hour per weight of catalyst therein may rangefrom 0.2 to 20. I

The oil vapors'after passing through the bed of catalytic materialwithin the reactor I8 may be passed into a cyclone separator 2Ipositioned in the top of the reactor for removing the relatively smallamount of entrained solids contained in the vapors. The vaporousconversion products after passing through the cyclone separator 2| areremoved overhead through line 22 and are passed to a fractionating tower23 wherein the vapors are subjected to fractionation. The higher boilingcondensate fraction formed in the bottom section of the fractionatingtower 23 normally contains a small amount of entrained catalyticmaterial. This initially condensing fraction may be withdrawn from thebottom of the fractionating tower 23 through line 24 and may be recycledthrough line 25 and pump 26 to line H where it merges with freshcharging stock and catalyst passing to the reactor I8. In some cases itmay be desirable to filter or otherwise concentrate the catalyticmaterial contained in the oil and return only the catalytic material tothe conversion zone. If desired, the bottom fraction from thefractionating tower may be withdrawn from the process through line 21.Also a portion of the bottom fraction may be passed through heatexchanger 29 where it is cooled and thereafter introduced into thefractionating tower through line 3I above the point of entry of thevapors therein to serve as a cooling and scrubbing medium for thevapors. the upper section of the fractionating tower 23 may be withdrawnthrough line 3|. Vapors remaining uncondensed in the fractionating tower23 pass overhead through line 32 to a condenser 33 wherein the desireddistillate is condensed. Products from the condenser 33 then pass to aproduct receiver 34 wherein the liquid distillate separates from theuncondensed vapors and gases. The liquid distillate is withdrawn fromthe receiver 34 through line 35 as a product of the process. A portionof the distillate may be returned to the bubble tower in order toprovide cooling for reflux. The distillate may be subjected to anyfurther finishing treatment desired to obtain the final market product.Vapors separated from the liquid distillate in the receiver 34 areremoved overhead through line 36 having a valve 36' for maintaining thedesired back pressure on the system. These gases may be passed tosuitable absorption and fractionating equipment for separation andfractionation. The pressure maintained within the reactor I8, in thecase of catalytic cracking, is preferably substantially atmospheric butmay be mild s uperatmospheric up I to 100 pounds per square inch.

Referring to the reactor I8, the bottom thereof communicates withconduit 31 which forms a second vertical column or standpipe forgenerating additional pressure on the catalyst for circulation. Thespace around the distributing cone I9 and the wall of the vessel and thebottom portion of the reactor below the cone may serve as a strippingzone in which catalytic material to be withdrawn is subjected tostripping treat- Condensate formed in ment with a purging gas to removevolatilizable' reaction products from the catalyst before discharginginto the air stream, as later described.

A stream of catalyst is continuously withdrawn from the bottom sectionof the reactor l8 through vertical standpipe 31 and discharges through avalve 38 into a stream of airpassing through line 39 which conveys itinto the bot: tom section of the regenerator l3.

The present invention deals particularly with a method for removing thevolatilizable reaction products from thecatalyst being withdrawn fromthe reactor it. In accordance with the present invention, there isinjected into the stream of catalyst passing through column '31 alimited quantity of air. This air is introduced into the column at apoint below the main stripping zone which, as illustrated, is located inthe bottom section 01 the reactor. The amount of air introduced into thevertical column is more than sufficient to fluidize the catalyst and isadequate to obtain the desired stripping of the volatilizable productstherefrom.

It has been found that the amount of carbon contained on the catalystwithdrawn from the reactor i8 is such that the oxygen contained in theair introduced into the column til is substantially completely andquickly combined with the carbon to form the oxides of carbon. Theamount of air introduced into the conduit 37 through lines ll, 52 andtie should be in excess of the minimum required for aeration but shouldbe limited to that which will rapidly combine with the carbon containedon the catalyst at the point of introduction of the air therein to formcom- 1 bustion gases substantially devoid of oxygen.

The amount of gas necessary for fluidizing or aerating the column 3? maybe defined as that necessary-to compensate for the shrinkage in volumeof gas intermixed with the catalyst passing through the standpipe.Unless some excess gas over and above that necessary to compensate forsuch shrinkage is supplied, the standpipe S'l cannot function forstripping the volatilizable hydrocarbons or other reaction products fromthe catalyst. In commercial operations the amount of air introduced intothe column 3? may be sumcient to give a superficial velocity of gasthrough the column of the order of from 0.2 to 2 feet per second. Theterm "superficial velocity" as herein employed means the velocity whichthe gas would attain in the absence of finely divided solids within thecolumn. By maintaining the superficial velocity of the gas streampassing through the catalytic material in th column d'l within thisrange, substantial stripping can b obtained within the column by thespent combustion gases formed by burning of the carbon with the airintroduced through the' spaced points an, 62 and d3.

Expressed in another way, the catalytic material flowing downwardly fromthe bottom of the reactor into the standpipe is contacted with a risingstream of spent combustion gases resulting from the reaction of the airintroduced at one or more spaced points ii, M and 33 with thecarbonaceous deposits contained on the catalytic material. Th lowerportion of standpipe or column 31 into which the air is introducedthereby forms an inert gas producer so that the gases removed from theupper end of the column and passing into the reactor l8 aresubstantially devoid of free oxygen. The standpipe 31 also serves toeffect a small degree of regeneration and this reduces the amount ofregeneration necessary to be carried out in the reactor l3.

The bottom portion oi the regenerator [3 may be in the form of aconeforming adistributing zone for the suspension of catalyst and airintroduced through line 39. A perforated grid 44 may be provided abovethe conical bottom through which the suspension of air and catalyst isinjected into the main portion of the regenerator it. The velocity ofthe regeneration. gas rising through the regenerator i3 is preferablycontrolled in the same manner as in the case oi! the vapors in thereactor it to permit the catalyst to segregate into a relatively dense,turbulent layer in the bottom portion of the regenerator it. To thisend. the superficial velocity of the rising gases may be of the order offrom 0.5 to 3 feet per second, depending upon the size and density'oithe catalytic material. The catalyst is retained within the regeneratorin contact with the oxidizing gas for a period sumcient to burn apredetermined portion of the carbonaceous deposits therefrom. A streamof regenerated catalyst continuously collects in a central compartmentlocated in the bottom of the regenerator which is in open communicationwith the vertical conduit or standpipe it previously described so thatthe regenerated catalyst continuously discharges baclr into the oilstream.

The spent combustion gases after passing through the bed of catalyticmaterial undergoing regeneration within the regenerator is may be passedto a cyclone separator tit positioned in the upper part of theregenerator for removal of entrained catalyst therefrom. It is usually Ipreferred to maintain the level of the catalyst within the regeneratorit at a substantial distance below the cyclone separator 36, such as amatter of from 5 to 15 feet, so as to reduce or minimize the amount ofpowder retained in the regeneration gas passing to the .cyclone,. Thespent regeneration gas is removed from the cyclone separator is throughline d'i and may be passed to further catalyst recovery equipment suchas scrubbers, bag filters, Cottrell precipitators, or the like which,for purposes of simplicity, have not been shown on the drawing.Furthermore, prior to passing to such further separating equipment, theregeneration gas may be cooled either by passing to suitable heatexchange equipment in a manner well known in the art or by injection ofwater, or both.

Referring to the reactor is, the level of the dense, turbulent layer ofcatalytic material therein is also preferably maintained a substantialdistance below the cyclone separator 2i so as to reduce the amount ofentrained catalyst carried into the cyclone separator 2| by the vaporousproducts.

While I have shown and described a, fluid catalyst process in which thestripping and purging of the spent catalyst are carried out principallyin the spent catalyst standpipe used for generating pressure, a separatetower independent of the be positioned immediately above the standpipe,

\ or the catalyst may be transferred from the bottom of the strippingtower into the top of the V standpipe by means of a carrier gas. In thlatter case, additional separators are provided for separating catalystfrom the stripping gas.

Furthermore, the invention in its broader phases is not limited to thefluid process but could be applied to a moving bed type processpreviously described. In any case, the stripping tower should beconsiderably longer than the diameter.; The lengthof the stripping toweris preferably from 3 to 8 tower diameters.

While the invention has been described as applied to the catalyticcracking of hydrocarbon oils employing the fluid catalyst process, itwill be understood that some of the broader phases of the invention arenot so limited.

Whatis desired to be protected by Letters Patent is:

l. A, process for cracking hydrocarbon oils which comprises passing theoil to be cracked through a cracking zone, passing a subdivided crackingcatalyst through said cracking zone in contact with said oil,maintaining said oil in contact with said catalyst at a temperature andfor a period sumcient to obtain substantial cracking thereof, thereafterremoving the vaporous conversion products from said zone, continuouslyremoving a stream of said subdivided cracking catalyst from said zonecontaining appreciable amounts of vaporous conversion products andcombustible deposits, passing the stream so withdrawn downwardly througha vertical column, introducing an oxidizing gas into the bttom portionof said column, controlling the amount of oxidizing gas so introduced sothat the oxygen is rapidly and completely consumed by burning a portionof the combustible deposits contained on said catalytic material,passing the resulting combustion gases substantially devoid of freeoxygen upwardly through said column to strip and replace the vaporousconversion products from the catalyst, removing catalyst from the baseof said column and transferring thecatalyst so removed into aregenerating zone, passing an oxidizing gas through said regeneratingzone, maintaining said catalyst within said regenerating zone in contactwith said catalyst for -a substantial period to burn additional amountsof combustible deposits therefrom, and thereafter returning the hOtregenerated catalyst to the cracking zone.

2. A process for the conversion of hydrocarbon oilswhich comprisespassing a stream of oil vaporsv upwardly through a conversion zonecontaining finely divided conversion catalyst, passing the vaporsupwardly through said conversion zone at a velocity controlled tomaintain a relatively dense, turbulent layer of finely divided catalyticmaterial in the bottom portion of said conversion zone, maintaining saidconversion zone at the desired conversion temperature, removing vaporousconversion products from the upper portion of said conversion zone,fractionating the vaporous conversion products to separate a desiredproduct therefrom, continuously withdrawing a stream of catalyticmaterial containing appreciable amounts of vapors conversion products 8tion within said regenerating zone to remove additional amounts ofcombustible deposits therefrom, and returning the regenerated catalystto the conversion zone.

3. A process for cracking hydrocarbon oils which comprise passing theoil in vapor form upwardly through a cracking zone containing a body offinely divided cracking catalyst, controling the velocity of the oilvapors passing upwardly through said cracking zone to maintain arelatively dense, turbulent body of catalyst in the bottom portion ofsaid cracking zone, maintaining said .011 vapors in contact with saidcatalyst within the cracking zone for a period sufiicient to obtainsubstantial cracking thereof, removing a relatively dense stream ofcatalyst containing appreciable amounts of vaporous conversion productsand solid combustible deposits from the bottom portion of said crackingzone, passing said stream of catalyst so removed downwardly through avertical column maintained substantially full of said catalyst,introducing a stream of air into the bottom portion of said column,limiting the amount of air so introduced toconsume rapidly andcompletely the oxygen contained therein by burning of carbonaceousdeposits contained on said catalyst, passing the stream of combustiongases upwardly through said column at a velocity controlled to strip andreplace vaporous conversion products from the stream of catalyst soremoved, passing the catalyst from the base of said column into aregenerating zone, passing a stream of oxidizing gas upwardly throughsaid regenerating zone at a velocity controlled to maintain a relativelydense, turbulent layer of catalytic material therein,

' maintaining said catalyst in contact with said andsolid combustibledeposits from the bottom portion of said conversion zone, passing saidstream of finely divided catalyst so-withdrawn downwardly through avertical column maintained substantially full of said catalyticmaterial, introducing a stream of air into the bottom of said column,controlling the amount of air so introduced to cause rapid and completeconsumption of said air and to form a combustion gas substantiallydevoid of free oxygen, passing the combus ion gas upwardly through saidcolumn to efiect replacement of vaporous conversion products from thecatalyst, passing catalyst from the base of said column into aregenerating zone, subjecting the catalyst to further regeneraoxidizinggas within the regenerating zone for a period sufllclent to remove asubstantial portion of combustible deposits contained thereon, and

thereafter returning the hot regenerated catalyst.

to the cracking zone.

4. A process according to claim 2 wherein the catalytic material iswithdrawn in a dense phase and passed to the upper part of said columnwherein the catalytic material is maintained in a dense fluidizedcondition.

5. A process according to claim 2 wherein the catalytic material iswithdrawn in a dense phase and passed to the upper part of said columnwherein the catalytic material is maintained in a dense fluidizedcondition and the stripped-out material and combustion gases pass intosaid conversion zone.

6. A process for the conversion of carbonaceous material which comprisespassing said material through a conversion zone, passing 'a subdividedconversion catalyst through said zone in contact with said carbonaceousmaterial, removing vaporous conversion products from said zone, removinga stream of subdivided conversion catalyst containing solid combustibledeposits and associated with a small amount of vaporous conversionproducts from said zone, passing an oxidizing gas in countercurrentcontact with said stream, limitous conversion products associated withsaid catalyst, thereafter passing the stream of catalyst to aregeneration zone and contacting the catalyst in said regeneration zonewith a fresh supply of oxidizing gas separate and independent from saidfirst-named oxidizing gas.

CHARLES w. TYSON.

REFERENCES CITED UNITED STATES PATENTS Name Date Voorhees Feb. 17, 1942Number Number 15 Number Name Date Prickett July 7, 1942 Degnen et ai..-Juiy 21, 1942 Arveson Dec. 1, 1942 Munday Feb. 16. 1943 Thomas et a1"Sept. 12, 1944 Wolk et a1 Apr. 17, 1945 Johnson Jan. 16. 1945 OdellDec. 18, 1934 Becker Apr. 8, 1945 Carlsmith Jan. 1, 1948 Bailey, et a].Sept. 3, 19.46

FOREIGN PATENTS Country Date Australia Apr. 27. 1944

